Semiconductor chips are manufactured by repeating many processing steps such as depositing, exposing, etching, and polishing on semiconductor substrates such as wafers. Specific conditions are suitable for the processing steps. The processing conditions include the processing environments for wafers during operations or in processing rooms. Important processing conditions include the wafer temperature during processing operations, temperature and pressure in processing chambers, high-frequency power applied to electrode plates, and quantities of processing gases. Insufficient processing condition and lack of stability may raise the rates of defects on semiconductor chips. For example, if a dry etching process is carried out in conditions outside the suitable range, degradation of etch rate and uniformity may occur.
Temperature-adjusting units such as chillers are usually employed to meet the temperature requirements for processing. Chillers function to maintain constant wafer temperature by cooling down an electrode plate or heating up a chamber during processing, preventing wafer breakage and processing failure due to hot temperature.
Chillers have a compressor, a condenser, an expansion valve, and an evaporator in which thermal exchange occurs between a refrigerant and cooling fluid. The amount of refrigerant supplied into the evaporator is variable in accordance with the kind of expansion valve, which affects the temperature of the cooling fluid a great deal. The processing temperature required in a processing chamber also varies in accordance with kinds of processing steps. For example, in an etching process, the processing temperature varies with the type of film material to be etched. When the material to be etched is an oxide, the wafer temperature is typically maintained at about −30° C. When the material to be etched is polycrystalline silicon, the wafer temperature is typically maintained at about 20° C. If the material to be etched is a metal, the wafer temperature is typically maintained at about 60° C.
A semiconductor chip is completed by depositing oxide films, polysilicon films, and metal films several times. Even with the same kinds of materials to be etched, the processing temperature may vary depending on sequential steps of deposition and correlations with lower films. Furthermore, there are large gaps of temperature among processing steps such as exposing, depositing, and etching in the processing chambers.
In handling a general apparatus, when the material to be etched changes, an operator exchanges the expansion valve for a new one that is adaptable to the processing temperature corresponding to the changed material, by way of a tuning operation on the chiller. However, the tuning results on the chillers may deviate with the individual operator, which reduces uniformity and reliability in processing the wafers. Thus, the practical processing steps typically cannot begin until after confirming whether the tuning operations have been properly accomplished in correspondence with the requirements for the processing conditions, resulting in degradation of the rate of operation.
Additionally, when high-frequency power is applied to a processing chamber, the temperature in the processing chamber may be affected by the high-frequency power. Since the tuning operations on the chillers are generally carried out without considering various factors influencing the processing steps, wafers may be put through processing steps without maintaining the appropriate processing temperature.
Furthermore, as the temperature of the processing chamber is regulated only by varying the amount of refrigerant supplied into the evaporator through the expansion valve during a process, it can be difficult precisely and accurately adjust the temperature of cooling fluid.